Firebase查询中有多个WHERE子句

Question

我正在尝试检索仅在到达日期和机场匹配时才返回飞行数据的数据。我似乎无法找出最佳解决方案。我只能在机场或到达日期相同的地方提取数据，而不能在两者都提取（只能使用equalTo()一次）。这是我当前的Java代码如下所示：

Firebase ref = mFirebaseRef.child(FirebaseReference.CHILD_FLIGHTS);

Query queryRef = ref.orderByChild("airport").equalTo(getAirport());

queryRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        System.out.println(TAG + " datasnapshot is equal to " + dataSnapshot);
    }
}

这是数据本身：

{
   "flight":{
      "1ddf3c02-1f2e-4eb7-93d8-3d8d4f9e3da2":{
         "airport":"Gothenburg, Sweden - Landvetter (GOT)",
         "arrivalDate":"2016-06-21",
         "arrivalTime":"20:58",
         "code":"GOT",
         "departureDate":"2016-06-23",
         "departureTime":"20:58"
      },
      "c2c86e54-b4d0-4d83-934b-775a86f0a16c":{
         "airport":"Gothenburg, Sweden - Landvetter (GOT)",
         "arrivalDate":"2016-06-21",
         "arrivalTime":"20:50",
         "code":"GOT",
         "departureDate":"2016-06-23",
         "departureTime":"20:50"
      }
   },
   "users":{
      "1ddf3c02-1f2e-4eb7-93d8-3d8d4f9e3da2":{
         "age":"25",
         "createdTime":"1466533088358",
         "email":"[e-mail]",
         "provider":"password",
         "sex":"M",
         "username":"user2"
      },
      "c2c86e54-b4d0-4d83-934b-775a86f0a16c":{
         "age":"25",
         "createdTime":"1466374588255",
         "email":"[e-mail]",
         "provider":"password",
         "sex":"M",
         "username":"user1"
      }
   }
}

当前的Java代码将返回 仅
具有相同机场的所有子级。如您所料，当客户端需要排序的数据量比上述测试数据大得多时，这是不可行的。如何更好地在Firebase端过滤数据？

Answer 1

实时数据库不支持多个where子句，但是您可以创建一个额外的密钥来使其成为可能。

A“飞行”在您的"flight"列表可以有一个组合键"arrivalDate"和"code"。

"1ddf3c02-1f2e-4eb7-93d8-3d8d4f9e3da2" : {
  "airport" : "Gothenburg, Sweden - Landvetter (GOT)",
  "arrivalDate" : "2016-06-21",
  "arrivalTime" : "20:58",
  "arrivalDate_code": "2016-06-21_GOT", // combined key
  "code" : "GOT",
  "departureDate" : "2016-06-23",
  "departureTime" : "20:58"
}

然后，您可以查询该密钥。

Firebase ref = mFirebaseRef.child(FirebaseReference.CHILD_FLIGHTS);
Query queryRef = ref.orderByChild("arrivalDate_code").equalTo("2016-06-21_GOT");
queryRef.addListenerForSingleValueEvent(new ValueEventListener() {
   @Override
   public void onDataChange(DataSnapshot dataSnapshot) {

   }
});

另一个选择是从数据结构的字段中取消：

/ flights
  / $code
    / $flight_id

这意味着您的数据将如下所示：

"flight" : {
  "GOT": {
    "1ddf3c02-1f2e-4eb7-93d8-3d8d4f9e3da2" : {
      "airport" : "Gothenburg, Sweden - Landvetter (GOT)",
      "arrivalDate" : "2016-06-21",
      "arrivalTime" : "20:58",
      "code" : "GOT",
      "departureDate" : "2016-06-23",
      "departureTime" : "20:58"
    }
  }
}

然后，您可以制定如下查询：

Firebase ref = mFirebaseRef.child(FirebaseReference.CHILD_FLIGHTS);
Query queryRef = ref.child("GOT").orderByChild("arrivalTime").equalTo("2016-06-21_GOT");
queryRef.addListenerForSingleValueEvent(new ValueEventListener() {
   @Override
   public void onDataChange(DataSnapshot dataSnapshot) {

   }
});